1. Field of the Invention
The present invention relates to an improvement in a liquid pressure control device for an anti-lock brake system, which is used as the braking apparatus for automobiles and other vehicles.
2. Description of the Prior Art
When the braking force applied to the automobile tires exceeds their road contact frictional force, the so-called brake lock phenomenon occurs, resulting in a loss of directional stability and an increase in the necessary braking distance. To avoid this phenomenon, it has been proposed to use a liquid pressure control device for an anti-lock brake system constructed with a control valve and a liquid pressure control piston. The control valve serves to interrupt the excessive liquid pressure in the braking circuit between the master cylinder and wheel cylinders. The liquid pressure control piston acts in conjunction with the control valve so as to control the liquid pressure to be fed to the wheel cylinders wherein the above mentioned liquid pressure control piston is actuated by a device which detects the rotating status of the wheels in such a manner that the liquid feed is interrupted just before the brakes lock and controlled to achieve the anti-locking effect. Such a construction is described, for example, in Japanese Laid Open Patent Application No. 48-96993. However, this construction has the disadvantage that the liquid pressure control piston can mis-function and the interruption by the control valve between the master cylinder and wheel cylinders can take place even if there is no brake lock phenomenon. Moreover, when the above-mentioned control valve is unexpectedly closed on the assembly line or during automobile repairs, a bleeding operation, in which air in the braking circuit is purged and brake liquid is charged, becomes difficult.